The impact of metallicity and X-rays on star formation

Star formation is regulated through a variety of feedback processes. In this study; we treat feedback by metal injection and a UV background as well as by X-ray irradiation. Our aim is to investigate whether star formation is significantly affected when the ISM of a proto-galaxxy enjoys different metallicities and when a star forming cloud resides in the vicinity of a strong X-ray source. We perform cosmological Enzo simulations with a detailed treatment of non-zero metallicity chemistry and thermal balance. We also perform FLASH simulations with embedded Lagrangian sink particles of a collapsing molecular cloud near a massive; 10(7) M-circle dot, black hole that produces X-ray radiation.We find that a multi-phase ISM forms for metallicites as small as 10(-4) Solar at z = 6, with higher (10(-2) Z(circle dot)) metallicities supporting a cold (<100 K) and dense (> 10(3) cm(-3)) phase at higher (z = 20) redshift. A star formation recipe based on the presence of a cold dense phase leads to a self-regulating mode in the presence of supernova and radiation feedback. We also find that when there is strong X-ray feedback a collapsing cloud fragments into larger clumps whereby fewer but more massive protostellar cores a,re formed. This is a consequence of the higher Jeans mass in the warm (50 K, due to ionization heating) molecular gas. Accretion processes dominate the mass function and a. near-flat, non-Salpeter IMF results.